Stalling out

We have a 1992 Pontiac firebird with TBI the mileage is 145049 that we got a month ago it runs great as long as you are moving when you come to a stop, stop light, or go in reverse, or set the cruise she goes about 60 then drops down then picks back up again, she stalls my husband has replace the fuel pump and sreen and some sensors my mind has drawn a blan but one goes on the side of the TBI and the other goes in the transmission the torgue converter something or other switch someone told my husband it was vacum lines we checked them and nothing was wrong some said it could be the pressue sensor(diaphram)